Currently, very little is known about HIV-infection in adolescents. The primary objective of this protocol is to identify, characterize, and co-enroll HIV-infected adolescents into existing and future ACTG (or other NIH-sponsored) HIV treatment protocols via the systematic and recurrent assessment of eligibility. The study also will assess the ability of adolescents to adhere to HIV treatment protocols, to discover which factors influence an adolescent's access to treatment protocols, and to describe the nature, stage, and progression of adolescent HIV-infection. This is a multi-centered, prospective, longitudinal , cohort study involving 250 HIV-infected adolescents 13 to 20 years of age. Each enrollee will participate in ACTG 220 for a minimum of one year and a maximum of 4 years.